Countries like Hungary and Turkey are growing more corrupt as they become more autocratic, and threats to the American system of checks and balances have knocked the United States out of the top 20 “cleanest” countries, according to a closely watched annual survey released Tuesday.

Watchdog group Transparency International said its Corruption Perceptions Index for 2018 showed more than two-thirds of countries scoring below 50, on its scale where 100 is very clean and zero is very corrupt.

With a score of 71, the U.S. lost four points over 2017 and dropped out of the top 20 nations for the first time since 2011.

“A four point drop in the CPI score is a red flag and comes at a time when the U.S. is experiencing threats to its system of checks and balance, as well as an erosion of ethical norms at the highest levels of power,” the Berlin-based organization said.

“If this trend continues, it would indicate a serious corruption problem in a country that has taken a lead on the issue globally —this is a bipartisan issue that requires a bipartisan solution.”

In a cross-analysis of its survey with global democracy data, Transparency said a link could be drawn between corruption and the health of a democracy.

Full democracies scored an average of 75 on the corruption index, flawed democracies averaged 49, and autocratic regimes averaged 30, the organization said.

It noted that Hungary dropped eight points and Turkey nine over the past five years, to scores of 46 and 41, respectively.

At the same time, the report cited Freedom House’s annual democracy survey, noting Turkey was downgraded from “partly free” to “not free,” while Hungary registered its lowest score for political rights since the fall of communism in 1989.

The ratings reflect the “deterioration of rule of law and democratic institutions, as well as a rapidly shrinking space for civil society and independent media,” the organization said.

“Our research makes a clear link between having a healthy democracy and successfully fighting public sector corruption,” said Delia Ferreira Rubio, the head of Transparency. “Corruption is much more likely to flourish where democratic foundations are weak and, as we have seen in many countries, where undemocratic and populist politicians can use it to their advantage.”

Overall, Denmark led the survey as the least corrupt nation, with a score of 88, followed by New Zealand, Finland, Singapore, Sweden and Switzerland. Rounding out the top group were Norway, Netherlands, Canada, Luxembourg, Germany and Britain.

Somalia was rated the most corrupt with a score of 10, followed by Syria, South Sudan, Yemen, North Korea, Sudan, Guinea Bissau, Equatorial Guinea, Afghanistan and Libya.

Since 2012, only 20 nations had significantly improved their scores, including Argentina and Ivory Coast, which scored 40 and 35 respectively, up from 35 and 29.

At the same time, 16 have declined significantly in that time, including Australia, which slipped from a score of 85 to 77, and Chile, which dropped from 72 to 67.

The index is calculated using 13 different data sources that provide perceptions of public sector corruption from business people and country experts. These include the African Development Bank Country Policy and Institutional Assessment, the World Bank Country Policy and Institutional Assessment, the World Economic Forum Executive Opinion Survey and the World Justice Project Rule of Law Index Expert Survey.